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      <h1>Buildroot</h1>
    </div>

    <p><a href="http://buildroot.uclibc.org/">Buildroot</a>
    usage and documentation by Thomas Petazzoni. Contributions from
    Karsten Kruse, Ned Ludd, Martin Herren and others. </p>

    <p><small>$LastChangedDate: 2008-12-08 00:15:46 -0800 (Mon, 08 Dec 2008) $</small></p>

    <ul>

      <li><a href="#about">About Buildroot</a></li>
      <li><a href="#download">Obtaining Buildroot</a></li>
      <li><a href="#using">Using Buildroot</a></li>
      <li><a href="#custom_targetfs">Customizing the target filesystem</a></li>
      <li><a href="#custom_busybox">Customizing the Busybox
      configuration</a></li>
      <li><a href="#custom_uclibc">Customizing the uClibc
      configuration</a></li>
      <li><a href="#buildroot_innards">How Buildroot works</a></li>
      <li><a href="#using_toolchain">Using the uClibc toolchain</a></li>
      <li><a href="#toolchain_standalone">Using the uClibc toolchain
      outside of Buildroot</a></li>
      <li><a href="#downloaded_packages">Location of downloaded packages</a>
      </li>
      <li><a href="#add_software">Extending Buildroot with more
      Software</a></li>
      <li><a href="#links">Resources</a></li>
    </ul>

    <h2><a name="about" id="about"></a>About Buildroot</h2>

    <p>Buildroot is a set of Makefiles and patches that allow to easily
    generate both a cross-compilation toolchain and a root filesystem for your
    target. The cross-compilation toolchain uses uClibc (<a href=
    "http://www.uclibc.org/">http://www.uclibc.org/</a>), a tiny C standard
    library. </p>

    <p>Buildroot is useful mainly for people working with embedded systems.
    Embedded systems often use processors that are not the regular x86
    processors everyone is used to have on his PC. It can be PowerPC
    processors, MIPS processors, ARM processors, etc. </p>

    <p>A compilation toolchain is the set of tools that allows to
    compile code for your system. It consists of a compiler (in our
    case, <code>gcc</code>), binary utils like assembler and linker
    (in our case, <code>binutils</code>) and a C standard library (for
    example <a href="http://www.gnu.org/software/libc/libc.html">GNU
    Libc</a>, <a href="http://www.uclibc.org/">uClibc</a> or <a
    href="http://www.fefe.de/dietlibc/">dietlibc</a>). The system
    installed on your development station certainly already has a
    compilation toolchain that you can use to compile application that
    runs on your system. If you're using a PC, your compilation
    toolchain runs on an x86 processor and generates code for a x86
    processor. Under most Linux systems, the compilation toolchain
    uses the GNU libc as C standard library.  This compilation
    toolchain is called the &quot;host compilation toolchain&quot;, and more
    generally, the machine on which it is running, and on which you're
    working is called the &quot;host system&quot;. The compilation toolchain 
    is provided by your distribution, and Buildroot has nothing to do
    with it. </p>

    <p>As said above, the compilation toolchain that comes with your system
    runs and generates code for the processor of your host system. As your
    embedded system has a different processor, you need a cross-compilation
    toolchain: it's a compilation toolchain that runs on your host system but
    that generates code for your target system (and target processor). For
    example, if your host system uses x86 and your target system uses ARM, the
    regular compilation toolchain of your host runs on x86 and generates code
    for x86, while the cross-compilation toolchain runs on x86 and generates
    code for ARM. </p>

    <p>Even if your embedded system uses a x86 processor, you might interested
    in Buildroot, for two reasons:</p>

    <ul>
      <li>The compilation toolchain of your host certainly uses the GNU Libc
      which is a complete but huge C standard library. Instead of using GNU
      Libc on your target system, you can use uClibc which is a tiny C standard
      library. If you want to use this C library, then you need a compilation
      toolchain to generate binaries linked with it. Buildroot can do it for
      you. </li>

      <li>Buildroot automates the building of a root filesystem with all needed
      tools like busybox. It makes it much easier than doing it by hand. </li>
    </ul>

    <p>You might wonder why such a tool is needed when you can compile
    <code>gcc</code>, <code>binutils</code>, uClibc and all the tools by hand.
    Of course, doing so is possible. But dealing with all configure options,
    with all problems of every <code>gcc</code> or <code>binutils</code>
    version it very time-consuming and uninteresting. Buildroot automates this
    process through the use of Makefiles, and has a collection of patches for
    each <code>gcc</code> and <code>binutils</code> version to make them work
    on most architectures. </p>

    <h2><a name="download" id="download"></a>Obtaining Buildroot</h2>

    <p>Buildroot is available as daily SVN snapshots or directly using
    SVN. </p>

    <p>The latest snapshot is always available at <a
    href="http://buildroot.uclibc.org/downloads/snapshots/buildroot-snapshot.tar.bz2">http://buildroot.uclibc.org/downloads/snapshots/buildroot-snapshot.tar.bz2</a>,
    and previous snapshots are also available at <a
    href="http://buildroot.uclibc.org/downloads/snapshots/">http://buildroot.uclibc.org/downloads/snapshots/</a>. </p>

    <p>To download Buildroot using SVN, you can simply follow
    the rules described on the &quot;Accessing SVN&quot;-page (<a href=
    "http://buildroot.uclibc.org/subversion.html">http://buildroot.uclibc.org/subversion.html</a>)
    of the uClibc buildroot website (<a href=
    "http://buildroot.uclibc.org">http://buildroot.uclibc.org</a>), and download the
    <code>buildroot</code> SVN module. For the impatient, here's a quick
    recipe:</p>

 <pre>
 $ svn co svn://uclibc.org/trunk/buildroot
</pre>

    <h2><a name="using" id="using"></a>Using Buildroot</h2>

    <p>Buildroot has a nice configuration tool similar to the one you can find
    in the Linux Kernel (<a href=
    "http://www.kernel.org/">http://www.kernel.org/</a>) or in Busybox
    (<a href="http://www.busybox.org/">http://www.busybox.org/</a>). Note that
    you can build everything as a normal user. There is no need to be root to
    configure and use Buildroot. The first step is to run the configuration
    assistant:</p>

<pre>
 $ make menuconfig
</pre>

    <p>For each entry of the configuration tool, you can find associated help
    that describes the purpose of the entry. </p>

    <p>One of the key configuration items is the <code>PROJECT</code> which
    determines where some board specific packages are built and where the
    results are stored. </p>

    <p>Once everything is configured, the configuration tool has generated a
    <code>.config</code> file that contains the description of your
    configuration. It will be used by the Makefiles to do what's needed. </p>


    <p>Let's go:</p>

<pre>
 $ make
</pre>

    <p>This command will download, configure and compile all the selected
    tools, and finally generate a target filesystem. The target filesystem will
    be named <code>root_fs_ARCH.EXT</code> where <code>ARCH</code> is your
    architecture and <code>EXT</code> depends on the type of target filesystem
    selected in the <code>Target options</code> section of the configuration
    tool. 
    The file is stored in the "binaries/<code>$(PROJECT)</code>/" directory</p>

    <h3><a name="local_board_support" id="local_board_support"></a>
    Creating your own board support</h3>

    <p>Once a package has been unpacked, it is possible to manually update
    configuration files. Buildroot can automatically save the configuration
    of buildroot, linux, busybox, uclibc and u-boot in "local/$(PROJECT) by 
    using the command:
    </p>

<pre>
 $ make saveconfig
</pre>

     <p>Once a buildroot configuration has been created by saveconfig, 
     the default "$(TOPDIR)/.config" file can be overridden by</p>

<pre>
 $ make BOARD=&lt;project&gt;
</pre>

    <p>Buildroot will then use "local/&lt;project&gt;/&lt;project&gt;.config"
    instead of ".config". </p>

    <p>If you want to modify your board, you can copy the project configuration
     file to ".config" by using the command:</p> 

<pre>
 $ make BOARD=&lt;project&gt; getconfig
</pre>

    <p>You can share your custom board support directory between several buildroot trees
    by setting the environment variable <code>BUILDROOT_LOCAL</code> to this directory,
    </p> 


    <h3><a name="offline_builds" id="offline_builds"></a>
    Offline builds</h3>

    <p>If you intend to do an offline-build and just want to download all
    sources that you previously selected in &quot;make menuconfig&quot; then
    issue:</p>
<pre>
 $ make source
</pre>
    <p>You can now disconnect or copy the content of your <code>dl</code> 
    directory to the build-host. </p>

    <h3><a name="building_out_of_tree" id="building_out_of_tree"></a>
    Building out-of-tree</h3>

    <p>Buildroot supports building out of tree with a syntax similar
    to the Linux kernel. To use it, add O=&lt;directory&gt; to the
    make command line, E.G.:</p>

<pre>
 $ make O=/tmp/build
</pre>

    <p>And all the output files will be located under
    <code>/tmp/build</code>.</p>

    <h3><a name="environment_variables" id="environment_variables"></a>
    Environment variables</h3>

    <p>Buildroot optionally honors some environment variables that are passed
    to <code>make</code> :</p>
    <ul>
    <li>HOSTCXX</li>
    <li>HOSTCC</li>
    <li>UCLIBC_CONFIG_FILE=&lt;path/to/.config&gt;</li>
    <li>BUSYBOX_CONFIG_FILE=&lt;path/to/.config&gt;</li>
    </ul>

    <p>An example that uses config files located in the toplevel directory and
    in your $HOME:</p>
<pre>
$ make UCLIBC_CONFIG_FILE=uClibc.config BUSYBOX_CONFIG_FILE=$HOME/bb.config
</pre>

    <p>If you want to use a compiler other than the default <code>gcc</code>
    or <code>g++</code> for building helper-binaries on your host, then do</p>
<pre>
$ make HOSTCXX=g++-4.3-HEAD HOSTCC=gcc-4.3-HEAD
</pre>

    <h3><a name="helper_completion" id="helper_completion"></a>
    Using auto-completion</h3>

    <p>If you are lazy enough that you don't want to type the entire <i>make
    menuconfig</i> command line, you can enable auto-completion in your shell.
    Here is how you can do that using <i>bash</i>:</p>
<pre>
$ complete -W menuconfig make
</pre>

    <p>Then just enter the beginning of the line, and ask <i>bash</i> to
    complete it for you by pressing the <i>TAB</i> key:</p>
<pre>
$ make me&lt;TAB&gt;
</pre>

    <p>will result in <i>bash</i> to append <i>nuconfig</i> for you!</p>

    <p>Alternatively, some distributions (of which Debian and Mandriva are but
    an example) have more powerful make completion. Depending on you
    distribution, you may have to install a package to enable completion. Under
    Mandriva, this is <i>bash-completion</i>, while Debian ships it as part of
    the <i>bash</i> package.</p>

    <p>Other shells, such as <i>zsh</i>, also have completion facilities. See
    the documentation for your shell.</p>

    <h2><a name="custom_targetfs" id="custom_targetfs"></a>Customizing the
    target filesystem</h2>

    <p>There are a few ways to customize the resulting target filesystem:</p>

    <ul>
      <li>Customize the target filesystem directly, and rebuild the image. The
      target filesystem is available under <code>project_build_ARCH/root/</code>
      where <code>ARCH</code> is the chosen target architecture.
      You can simply make your changes here, and run make afterwards, which will
      rebuild the target filesystem image. This method allows to do everything 
      on the target filesystem, but if you decide to completely rebuild your 
      toolchain and tools, these changes will be lost. </li>

      <li>Customize the target filesystem skeleton, available under
      <code>target/generic/target_skeleton/</code>. You can customize
      configuration files or other stuff here. However, the full file hierarchy
      is not yet present, because it's created during the compilation process.
      So you can't do everything on this target filesystem skeleton, but
      changes to it remain even if you completely rebuild the cross-compilation
      toolchain and the tools. <br />
      You can also customize the <code>target/generic/device_table.txt</code>
      file which is used by the tools that generate the target filesystem image
      to properly set permissions and create device nodes. The
      <code>target/generic/skel.tar.gz</code> file contains the main
      directories of a root filesystem and there is no obvious reason for which
      it should be changed. These main directories are in an tarball inside of
      inside the skeleton because it contains symlinks that would be broken
      otherwise. <br />
      These customizations are deployed into 
      <code>project_build_ARCH/root/</code> just before the actual image
      is made. So simply rebuilding the image by running
      make should propagate any new changes to the image. </li>

      <li>When configuring the build system, using <code>make menuconfig</code>,
      you can specify the contents of the /etc/hostname and /etc/issue
      (the welcome banner) in the <code>PROJECT</code> section</li>
    </ul>

    <h2><a name="custom_busybox" id="custom_busybox"></a>Customizing the
    Busybox configuration</h2>

    <p><a href="http://www.busybox.net/">Busybox</a> is very configurable, and
    you may want to customize it. You can
    follow these simple steps to do it. It's not an optimal way, but it's
    simple and it works. </p>

    <ol>
      <li>Make a first compilation of buildroot with busybox without trying to
      customize it. </li>

      <li>Invoke <code>make busybox-menuconfig</code>.
      The nice configuration tool appears and you can
      customize everything. </li>

      <li>Run the compilation of buildroot again. </li>
    </ol>

    <p>Otherwise, you can simply change the
    <code>package/busybox/busybox-&lt;version&gt;.config</code> file if you 
    know the options you want to change without using the configuration tool.
    </p>
    <p>If you want to use an existing config file for busybox, then see 
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="custom_uclibc" id="custom_uclibc"></a>Customizing the uClibc
    configuration</h2>

    <p>Just like <a href="#custom_busybox">BusyBox</a>, <a
    href="http://www.uclibc.org/">uClibc</a> offers a lot of
    configuration options. They allow to select various
    functionalities, depending on your needs and limitations. </p>

    <p>The easiest way to modify the configuration of uClibc is to
    follow these steps :</p>

    <ol>

      <li>Make a first compilation of buildroot without trying to
      customize uClibc. </li>

      <li>Invoke <code>make uclibc-menuconfig</code>.
      The nice configuration assistant, similar to
      the one used in the Linux Kernel or in Buildroot appears. Make
      your configuration as appropriate. </li>

      <li>Copy the <code>.config</code> file to
      <code>toolchain/uClibc/uClibc.config</code> or
      <code>toolchain/uClibc/uClibc.config-locale</code>. The former
      is used if you haven't selected locale support in Buildroot
      configuration, and the latter is used if you have selected
      locale support. </li>

      <li>Run the compilation of Buildroot again</li>

    </ol>

    <p>Otherwise, you can simply change
    <code>toolchain/uClibc/uClibc.config</code> or
    <code>toolchain/uClibc/uClibc.config-locale</code> without running
    the configuration assistant. </p>

    <p>If you want to use an existing config file for uclibc, then see 
    section <a href="#environment_variables">environment variables</a>. </p>

    <h2><a name="buildroot_innards" id="buildroot_innards"></a>How Buildroot
    works</h2>

    <p>As said above, Buildroot is basically a set of Makefiles that download,
    configure and compiles software with the correct options. It also includes
    some patches for various software, mainly the ones involved in the
    cross-compilation tool chain (<code>gcc</code>, <code>binutils</code> and
    uClibc). </p>

    <p>There is basically one Makefile per software, and they are named with
    the <code>.mk</code> extension. Makefiles are split into four
    sections:</p>

    <ul>
      <li><b>project</b> (in the <code>project/</code> directory) contains
      the Makefiles and associated files for all software related to the
      building several root file systems in the same buildroot tree. </li>

      <li><b>toolchain</b> (in the <code>toolchain/</code> directory) contains
      the Makefiles and associated files for all software related to the
      cross-compilation toolchain : <code>binutils</code>, <code>ccache</code>,
      <code>gcc</code>, <code>gdb</code>, <code>kernel-headers</code> and
      <code>uClibc</code>. </li>

      <li><b>package</b> (in the <code>package/</code> directory) contains the
      Makefiles and associated files for all user-space tools that Buildroot
      can compile and add to the target root filesystem. There is one
      sub-directory per tool. </li>

      <li><b>target</b> (in the <code>target</code> directory) contains the
      Makefiles and associated files for software related to the generation of
      the target root filesystem image. Four types of filesystems are supported
      : ext2, jffs2, cramfs and squashfs. For each of them, there's a
      sub-directory with the required files. There is also a
      <code>default/</code> directory that contains the target filesystem
      skeleton. </li>
    </ul>

    <p>Each directory contains at least 2 files :</p>

    <ul>
      <li><code>something.mk</code> is the Makefile that downloads, configures,
      compiles and installs the software <code>something</code>. </li>

      <li><code>Config.in</code> is a part of the configuration tool
      description file. It describes the option related to the current
      software. </li>

    </ul>

    <p>The main Makefile do the job through the following steps (once the
    configuration is done):</p>

    <ol>
      <li>Create the download directory (<code>dl/</code> by default). This is
      where the tarballs will be downloaded. It is interesting to know that the
      tarballs are in this directory because it may be useful to save them
      somewhere to avoid further downloads. </li>

      <li>Create the shared build directory (<code>build_ARCH/</code> by
      default, where <code>ARCH</code> is your architecture). This is where all
      non configurable user-space tools will be compiled.When building two or
      more targets using the same architecture, the first build will go through 
      the full download, configure, make process, but the second and later 
      builds will only copy the result from the first build to its project 
      specific target directory significantly speeding up the build process</li>

      <li>Create the project specific build directory 
      (<code>project_build_ARCH/$(PROJECT)</code> by default, where 
      <code>ARCH</code> is your architecture). This is where all configurable 
      user-space tools will be compiled. The project specific build directory 
      is neccessary, if two different targets needs to use a specific package, 
      but the packages have different configuration for both targets. Some 
      examples of packages built in this directory are busybox and linux.
      </li>

      <li>Create the project specific result directory 
      (<code>binaries/$(PROJECT)</code> by default, where <code>ARCH</code> 
      is your architecture). This is where the root filesystem images are
      stored, It is also used to store the linux kernel image and any 
      utilities, boot-loaders etc. needed for a target.
      </li>

      <li>Create the toolchain build directory
      (<code>toolchain_build_ARCH/</code> by default, where <code>ARCH</code>
      is your architecture). This is where the cross compilation toolchain will
      be compiled. </li>

      <li>Setup the staging directory (<code>build_ARCH/staging_dir/</code> by
      default). This is where the cross-compilation toolchain will be
      installed. If you want to use the same cross-compilation toolchain for
      other purposes, such as compiling third-party applications, you can add
      <code>build_ARCH/staging_dir/usr/bin</code> to your PATH, and then use
      <code>arch-linux-gcc</code> to compile your application. In order to
      setup this staging directory, it first removes it, and then it creates
      various subdirectories and symlinks inside it. </li>

      <li>Create the target directory (<code>project_build_ARCH/root/</code> by
      default) and the target filesystem skeleton. This directory will contain
      the final root filesystem. To setup it up, it first deletes it, then it
      uncompress the <code>target/generic/skel.tar.gz</code> file to create the
      main subdirectories and symlinks, copies the skeleton available in
      <code>target/generic/target_skeleton</code> and then removes useless
      <code>.svn/</code> directories. </li>

      <li>Add the <code>TARGETS</code> dependency. This should generally check
      if the configuration option for this package is enabled, and if so then
      &quot;subscribe&quot; this package to be compiled by adding it to the
      TARGETS global variable. </li>
    </ol>

    <h2><a name="multi_project" id="multi_project"></a>Building several
      projects in the same buildroot source tree</h2>

    <p><b>BACKGROUND</b></p>

    <p>Buildroot has always supported building several projects in the same
    tree if each project was for a different architecture. </p>

    <p>The root file system has been created in the 
    <code>&quot;build_&lt;ARCH&gt;/root&quot;</code>
    directory which is unique for each architecture. 
    Toolchains have been built in
    <code>&quot;toolchain_build_&lt;ARCH&gt;&quot;</code>. </p>

    <p> It the user wanted to build several root file systems for the same
    architecture, a prefix or suffix could be added in the configuration file
    so the root file system would be built in
    <code>&quot;&lt;PREFIX&gt;_build_&lt;ARCH&gt;_&lt;SUFFIX&gt;/root&quot;</code>
    By supplying <u>unique</u> combinations of 
    <code>&quot;&lt;PREFIX&gt;&quot;</code> and
    <code>&quot;&lt;SUFFIX&gt;&quot;</code>
    each project would get a <u>unique</u> root file system tree. </p>

    <p>The disadvantage of this approach is that a new toolchain was
    built for each project,  adding considerable time to the build
    process, even if it was two projects for the same chip. </p>

    <p>This drawback has been somewhat lessened with 
    <code>gcc-4.x.y</code> which allows buildroot to use an external 
    toolchain. Certain packages requires special
    features in the toolchain, and if an external toolchain is selected,
    this may lack the neccessary features to complete the build of the root
     file system.</p>

    <p>A bigger problem was that the 
    <code>&quot;build_&lt;ARCH&gt;&quot;</code> tree
    was also duplicated, so each </code>package</code> would also
    be rebuilt once per project, resulting in even longer build times.</p>


    <p><b>PROJECT TO SHARE TOOLCHAIN AND PACKAGE BUILDS</b></p>

    <p>Work has started on a project which will allow the user to build 
    multiple root file systems for the same architecture in the same tree. 
    The toolchain and the package build directory will be shared, but each
    project will have a dedicated directory tree for project specific
    builds. </p>

    <p>With this approach, most, if not all packages will be compiled 
    when the first project is built.
    The process is almost identical to the original process.
    Packages are downloaded and extracted to the shared 
    <code>&quot;build_&lt;ARCH&gt;/&lt;package&gt;&quot;</code>
    directory. They are configured and compiled. </p> 

    <p>Package libraries and headers are installed in the shared $(STAGING_DIR),
    and then the project specific root file system &quot;$(TARGET_DIR)&quot;
    is populated. </p> 

    <p>At the end of the build, the root file system will be used
    to generate the resulting root file system binaries. </p>

    <p>Once the first project has been built, building other projects will 
    typically involve populating the new project's root file system directory
    from the existing binaries generated in the shared 
    <code>&quot;build_&lt;ARCH&gt;/&lt;&gt;&quot;</code> directory. </p>

    <p>Only packages, not used by the first project, will have to go
    through the normal extract-configure-compile flow. </p>

    <p><b>IMPLEMENTATION</b></p>

    <p>The core of the solution is the introduction
    of two new directories: </p>

    <ul>
    <li><code>project_build_&lt;ARCH&gt;</code></li>

    <li><code>binaries;</code></li>
    </ul>

    <p>Each of the directories contain one subdirectory per project. 
    The name of the subdirectory is configured by the user in the 
    normal buildroot configuration, using the value of: </p>

    <p><code>Project Options ---> Project name</code></p>

    <p>The configuration defines the $(PROJECT) variable.</p>

    <p>The default project name is <code>&quot;uclibc&quot;</code>.</p>

    <p><code>&quot;package/Makefile.in&quot;</code> defines:
    <pre>
    <code>PROJECT_BUILD_DIR:=project_build_$(ARCH)/$(PROJECT)</code>
    <code>BINARIES_DIR:=binaries/$(PROJECT)</code>
    </pre>
    </p>

    <p>It also defines the location for the target root file system:
    <pre>
    <code>TARGET_DIR:=$(PROJECT_BUILD_DIR)/$(PROJECT)/root</code>
    </pre>
    </p>

    <p>I.E: If the user has choosen
    <code>&quot;myproject&quot;</code>
    as the $(PROJECT) name:

    <ul>
    <li><code>&quot;project_build_&lt;ARCH&gt;/myproject&quot;</code></li>
    <li><code>&quot;binaries/myproject&quot;</code></li>
    </ul>

    <p>will be created. </p>

    <p>Currently, the <u>root file system</u>, <u>busybox</u> and an Atmel
    customized version of  
    <u><code>U-Boot</code></u>, as well as some Atmel specific
    bootloaders like <u>at91-bootstrap</u> and <u>dataflashboot.bin</u>
    are built in 
    <code>&quot;$(PROJECT_BUILD_DIR)&quot;</code>

    <p>The resulting binaries for all architectures are stored in the 
    <code>&quot;$(BINARIES_DIR)&quot;</code> directory. <p>

    <p><b>SUMMARY</b></p>

    <p>The project will share directories which can be share without
    conflicts, but will use unique build directories, where the user
    can configure the build. </p>

    <p><b>THINGS TO DO</b></p>
    
    <ol>

    <li>Linux</li>

    <p>The current Linux implementation is flawed. It only works
    if the user chooses to use one of the few kernels selected 
    as base for the kernel-headers. While the Makefile seems to have
    hooks, allowing the developer to specify whatever version he/she
    wants in the target/device/*/* Makefiles, the build will fail
    if another kernel version is choosen.</p>

    <p>The reason for this is that the kernel patches are not
    applied by the <code>&quot;target/linux/linux.mk&quot;</code>
    build script fragment. They are only applied by the 
    <code>&quot;toolchain/kernel-headers/*.makefile&quot;</code>
    build script fragments</p>

    <p>If the kernel-header version and the linux version differs,
    there will be two <code>&quot;linux-2.6.X.Y&quot;</code>
    directories in 
    <code>&quot;build_&lt;ARCH&gt;/&lt;&gt;&quot;</code>,
    each with its own set of patches. </p>

    <p>The solution in the works, is to move the build of Linux to     
    <code>&quot;project_build_&lt;ARCH&gt;/&lt;project name&gt;/linux-2.6.X.Y&quot;</code> combined with method to configure
     which patches can be applied. Possibly, the linux source tree
     used to generate the kernel headers will be moved to the
     <code>&quot;toolchain_build_&lt;ARCH&gt;&quot;</code>
     directory
      </p>

     <p>The user will be able to select from three different
     Linux strategies:

     <ul>
     <li>Conservative Strategy: Only use version ssupported by the kernel headers</li>
     <li>Stable Linux Strategy: Allow any 2.6.X.Y combination.
	(Minimum 2.6.19)</li>
     <li>Power-User Strategy: Allow 
     <code>&quot;-git&quot;</code>, or
     <code>&quot;-mm&quot;</code>, or user downloadable kernels</li>
     </ul>

     <p>The current kernel patches can be configured to be applied to the
     linux source tree even if the version differs from the 
     kernel header version. </p>

     <p>Since the user can select any kernel-patch
     he/she will be able to select a non-working combination.
     If the patch fails, the user will have to generate a new 
     proprietary kernel-patch or decide to not apply the kernel
     patches</p>

     <p>Other optional patches will be <u>board specific</u> or
     <u>architecture specific</u> patches. </p>

     <p>There will also be a way for the user to supply absolute
     or relative paths to patches, possibly outside the main tree.
     This can be used to apply custom kernel-header-patches, if
     the versions available in buildroot cannot be applied to the 
     specific linux version used</p>

     <p>Maybe, there will also be a possibility to supply an 
     <code>&quot;URL&quot;</code> to a patch available on Internet. </p>

     <li>Configurable packages</li>

     <p>Many packages can, on top of the simple
     &quot;enable/disable build&quot;,
     be further configured using Kconfig.
     Currently these packages will be compiled using the 
     configuration specified in the
     <code>&quot;.config&quot;</code> file of the <u>first</u>
     project demanding the build of the package.</p>

     <p>If <u>another</u> project uses the same packages, but with 
     a different configuration,these packages will <u>not</u> be rebuilt,
     and the root file system for the new project will be populated
     with files from the build of the <u>first</u> project</p>

     <p>If multiple project are built, and a specific package
     needs two different configuration, then the user must
     delete the package from the
     <code>&quot;build_&lt;ARCH&gt;&quot;</code> directory
     before rebuilding the new project.<p>

     <p>A long term solution is to edit the package makefile and move 
     the build of the configurable packages from 
     <code>&quot;build_&lt;ARCH&gt;&quot;</code> to
     <code>&quot;project_build_&lt;ARCH&gt;/&lt;project name&gt;&quot;</code>
     and send a patch to the buildroot mailing list.

     <li>Naming conventions</li>

     <p>Names of resulting binaries should reflect the
     &quot;project name&quot;

     <li>Generating File System binaries</li>
     <p>
     Packages which needs to be installed with the &quot;root&quot;
     as owner, will generate a 
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code> file
     which will be used for the final build of the root file system binary. </p>

     <p>This was previously located in the 
     <code>&quot;$(STAGING_DIR)&quot;</code> directory, but was
     recently moved to the 
     <code>&quot;$(PROJECT_BUILD_DIR)&quot;</code> directory. </p>

     <p>Currently only three packages: 
     <code>&quot;at&quot;</code>,
     <code>&quot;ltp-testsuite&quot;</code> and
     <code>&quot;nfs-utils&quot;</code>
     requests fakeroot. <p>

     <p>The makefile fragments for each file system type like
     <code>&quot;ext2&quot;</code>,
     <code>&quot;jffs2&quot;</code> or
     <code>&quot;squashfs&quot;</code>
     will, when the file system binary is generated,
     collect all present
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code> files
     to a single <code>&quot;_fakeroot.&lt;file system&gt;&quot;</code>
     file and call fakeroot.</p>
     <code>&quot;.fakeroot.&lt;package&gt;&quot;</code>
     files are deleted as the last action of the Buildroot Makefile. </p>

     <p>It needs to be evaluated if any further action for the 
     file system binary build is needed. </p>

     </ol>

    <h2><a name="using_toolchain" id="using_toolchain"></a>Using the
    uClibc toolchain</h2>

    <p>You may want to compile your own programs or other software
    that are not packaged in Buildroot. In order to do this, you can
    use the toolchain that was generated by Buildroot. </p>

    <p>The toolchain generated by Buildroot by default is located in
    <code>build_ARCH/staging_dir/</code>. The simplest way to use it
    is to add <code>build_ARCH/staging_dir/usr/bin/</code> to your PATH
    environnement variable, and then to use
    <code>arch-linux-gcc</code>, <code>arch-linux-objdump</code>,
    <code>arch-linux-ld</code>, etc. </p>

    <p>For example, you may add the following to your
    <code>.bashrc</code> (considering you're building for the MIPS
    architecture and that Buildroot is located in
    <code>~/buildroot/</code>) :</p>

<pre>
export PATH=&quot;$PATH:~/buildroot/build_mips/staging_dir/usr/bin/&quot;
</pre>

    <p>Then you can simply do :</p>

<pre>
mips-linux-gcc -o foo foo.c
</pre>

    <p><b>Important</b> : do not try to move a gcc-3.x toolchain to an other
    directory, it won't work. There are some hardcoded paths in the
    <i>gcc</i> configuration. If the default toolchain directory
    doesn't suit your needs, please refer to the <a
    href="#toolchain_standalone">Using the uClibc toolchain outside of
    buildroot</a> section. </p>
    <p>If you are using a current gcc-4.x, then use --sysroot and -isysroot
    since these toolchains have fully functional sysroot support. No
    hardcoded paths do exist in these configurations. </p>

    <h2><a name="toolchain_standalone" id="toolchain_standalone"></a>Using the
    uClibc toolchain outside of buildroot</h2>

    <p>By default, the cross-compilation toolchain is generated inside
    <code>build_ARCH/staging_dir/</code>. But sometimes, it may be useful to
    install it somewhere else, so that it can be used to compile other programs
    or by other users. Moving the <code>build_ARCH/staging_dir/</code>
    directory elsewhere is <b>not possible if using gcc-3.x</b>, because there
    are some hardcoded paths in the toolchain configuration. This works, thanks 
    to sysroot support, with current, stable gcc-4.x toolchains, of course. </p>

    <p>If you want to use the generated gcc-3.x toolchain for other purposes,
    you can configure Buildroot to generate it elsewhere using the
    option of the configuration tool : <code>Build options -&gt;
    Toolchain and header file location</code>, which defaults to
    <code>$(BUILD_DIR)/staging_dir/</code>. </p>

    <h2><a name="downloaded_packages"
    id="downloaded_packages"></a>Location of downloaded packages</h2>

    <p>It might be useful to know that the various tarballs that are
    downloaded by the <i>Makefiles</i> are all stored in the
    <code>DL_DIR</code> which by default is the <code>dl</code>
    directory. It's useful for example if you want to keep a complete
    version of Buildroot which is know to be working with the
    associated tarballs. This will allow you to regenerate the
    toolchain and the target filesystem with exactly the same
    versions. </p>

    <p>If you maintain several buildroot trees, it might be better to have
    a shared download location. This can be accessed by creating a symbolic link
    from the <code>dl</code> directory to the shared download location. </p>

    <p>I.E:</p>

<pre>
ln -s &lt;shared download location&gt; dl
</pre>

    <p>Another way of accessing a shared download location is to
    create the <code>BUILDROOT_DL_DIR</code> environment variable.
    If this is set, then the value of DL_DIR in the project is
    overridden. The following line should be added to 
    <code>&quot;~/.bashrc&quot;</code>. <p>

<pre>
export BUILDROOT_DL_DIR &lt;shared download location&gt;
</pre>



    <h2><a name="add_software" id="add_software"></a>Extending Buildroot with
    more software</h2>

    <p>This section will only consider the case in which you want to
    add user-space software. </p>

    <h3>Package directory</h3>

    <p>First of all, create a directory under the <code>package</code>
    directory for your software, for example <code>foo</code>. </p>

    <h3><code>Config.in</code> file</h3>

    <p>Then, create a file named <code>Config.in</code>. This file
    will contain the portion of options description related to our
    <code>foo</code> software that will be used and displayed in the
    configuration tool. It should basically contain :</p>

<pre>
config BR2_PACKAGE_FOO
        bool "foo"
        help
	  This is a comment that explains what foo is.

	  http://foosoftware.org/foo/
</pre>

    <p>Of course, you can add other options to configure particular
    things in your software. </p>
    <p>Finally you have to add your new <code>foo/Config.in</code> to
    <code>package/Config.in</code>. The files included there are
    <em>sorted alphabetically</em> per category and are <em>NOT<em>
    supposed to contain anything but the <em>bare</em> name of the package.</p>
<pre>
if !BR2_PACKAGE_BUSYBOX_HIDE_OTHERS
source "package/procps/Config.in"
endif
</pre>
   <p><strong>Note:</strong><br>
   Generally all packages should live <em>directly</em> in the
   <code>package</code> directory to make it easier to find them.
   </p>
   <h3>The real <i>Makefile</i></h3>

   <p>Finally, here's the hardest part. Create a file named
   <code>foo.mk</code>. It will contain the <i>Makefile</i> rules that
   are in charge of downloading, configuring, compiling and installing
   the software. Below is an example that we will comment
   afterwards. </p>

<pre>
     <a name="line1" id="line1">1</a>  #############################################################
     <a name="line2" id="line2">2</a>  #
     <a name="line3" id="line3">3</a>  # foo
     <a name="line4" id="line4">4</a>  #
     <a name="line5" id="line5">5</a>  #############################################################
     <a name="line6" id="line6">6</a>  FOO_VERSION:=1.0
     <a name="line7" id="line7">7</a>  FOO_SOURCE:=foo-$(FOO_VERSION).tar.gz
     <a name="line8" id="line8">8</a>  FOO_SITE:=http://www.foosoftware.org/downloads
     <a name="line9" id="line9">9</a>  FOO_DIR:=$(BUILD_DIR)/foo-$(FOO_VERSION)
    <a name="line10" id="line10">10</a>  FOO_BINARY:=foo
    <a name="line11" id="line11">11</a>  FOO_TARGET_BINARY:=usr/bin/foo
    <a name="line12" id="line12">12</a>
    <a name="line13" id="line13">13</a>  $(DL_DIR)/$(FOO_SOURCE):
    <a name="line14" id="line14">14</a>          $(WGET) -P $(DL_DIR) $(FOO_SITE)/$(FOO_SOURCE)
    <a name="line15" id="line15">15</a>
    <a name="line16" id="line16">16</a>  $(FOO_DIR)/.source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="line17" id="line17">17</a>          $(ZCAT) $(DL_DIR)/$(FOO_SOURCE) | tar -C $(BUILD_DIR) $(TAR_OPTIONS) -
    <a name="line18" id="line18">18</a>          touch $@
    <a name="line19" id="line19">19</a>
    <a name="line20" id="line20">20</a>  $(FOO_DIR)/.configured: $(FOO_DIR)/.source
    <a name="line21" id="line21">21</a>          (cd $(FOO_DIR); rm -rf config.cache; \
    <a name="line22" id="line22">22</a>                  $(TARGET_CONFIGURE_OPTS) \
    <a name="line23" id="line23">23</a>                  $(TARGET_CONFIGURE_ARGS) \
    <a name="line24" id="line24">24</a>                  ./configure \
    <a name="line25" id="line25">25</a>                  --target=$(GNU_TARGET_NAME) \
    <a name="line26" id="line26">26</a>                  --host=$(GNU_TARGET_NAME) \
    <a name="line27" id="line27">27</a>                  --build=$(GNU_HOST_NAME) \
    <a name="line28" id="line28">28</a>                  --prefix=/usr \
    <a name="line29" id="line29">29</a>                  --sysconfdir=/etc \
    <a name="line30" id="line30">30</a>          )
    <a name="line31" id="line31">31</a>          touch $@
    <a name="line32" id="line32">32</a>
    <a name="line33" id="line33">33</a>  $(FOO_DIR)/$(FOO_BINARY): $(FOO_DIR)/.configured
    <a name="line34" id="line34">34</a>          $(MAKE) CC=$(TARGET_CC) -C $(FOO_DIR)
    <a name="line35" id="line35">35</a>
    <a name="line36" id="line36">36</a>  $(TARGET_DIR)/$(FOO_TARGET_BINARY): $(FOO_DIR)/$(FOO_BINARY)
    <a name="line37" id="line37">37</a>          $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) install
    <a name="line38" id="line38">38</a>          rm -Rf $(TARGET_DIR)/usr/man
    <a name="line39" id="line39">39</a>
    <a name="line40" id="line40">40</a>  foo: uclibc ncurses $(TARGET_DIR)/$(FOO_TARGET_BINARY)
    <a name="line41" id="line41">41</a>
    <a name="line42" id="line42">42</a>  foo-source: $(DL_DIR)/$(FOO_SOURCE)
    <a name="line43" id="line43">43</a>
    <a name="line44" id="line44">44</a>  foo-clean:
    <a name="line45" id="line45">45</a>          $(MAKE) prefix=$(TARGET_DIR)/usr -C $(FOO_DIR) uninstall
    <a name="line46" id="line46">46</a>          -$(MAKE) -C $(FOO_DIR) clean
    <a name="line47" id="line47">47</a>
    <a name="line48" id="line48">48</a>  foo-dirclean:
    <a name="line49" id="line49">49</a>          rm -rf $(FOO_DIR)
    <a name="line50" id="line50">50</a>
    <a name="line51" id="line51">51</a> #############################################################
    <a name="line52" id="line52">52</a> #
    <a name="line53" id="line53">53</a> # Toplevel Makefile options
    <a name="line54" id="line54">54</a> #
    <a name="line55" id="line55">55</a> #############################################################
    <a name="line56" id="line56">56</a> ifeq ($(BR2_PACKAGE_FOO),y)
    <a name="line57" id="line57">57</a> TARGETS+=foo
    <a name="line58" id="line58">58</a> endif

</pre>

    <p>First of all, this <i>Makefile</i> example works for a single
    binary software. For other software such as libraries or more
    complex stuff with multiple binaries, it should be adapted. Look at
    the other <code>*.mk</code> files in the <code>package</code>
    directory. </p>

    <p>At lines <a href="#line6">6-11</a>, a couple of useful variables are 
    defined :</p>

    <ul>

     <li><code>FOO_VERSION</code> : The version of <i>foo</i> that
     should be downloaded. </li>

     <li><code>FOO_SOURCE</code> : The name of the tarball of
     <i>foo</i> on the download website of FTP site. As you can see
     <code>FOO_VERSION</code> is used. </li>

     <li><code>FOO_SITE</code> : The HTTP or FTP site from which
     <i>foo</i> archive is downloaded. It must include the complete
     path to the directory where <code>FOO_SOURCE</code> can be
     found. </li>

     <li><code>FOO_DIR</code> : The directory into which the software
     will be configured and compiled. Basically, it's a subdirectory
     of <code>BUILD_DIR</code> which is created upon decompression of
     the tarball. </li>

     <li><code>FOO_BINARY</code> : Software binary name. As said
     previously, this is an example for a single binary software. </li>

     <li><code>FOO_TARGET_BINARY</code> : The full path of the binary
     inside the target filesystem. </li>

    </ul>

    <p>Lines <a href="#line13">13-14</a> defines a target that downloads the 
    tarball from the remote site to the download directory
    (<code>DL_DIR</code>). </p>

    <p>Lines <a href="#line16">16-18</a> defines a target and associated rules 
    that uncompress the downloaded tarball. As you can see, this target
    depends on the tarball file, so that the previous target (line
    <a href="#line13">13-14</a>) is called before executing the rules of the 
    current target. Uncompressing is followed by <i>touching</i> a hidden file
    to mark the software has having been uncompressed. This trick is
    used everywhere in Buildroot <i>Makefile</i> to split steps
    (download, uncompress, configure, compile, install) while still
    having correct dependencies. </p>

    <p>Lines <a href="#line20">20-31</a> defines a target and associated rules 
    that configures the software. It depends on the previous target (the
    hidden <code>.source</code> file) so that we are sure the software has
    been uncompressed. In order to configure it, it basically runs the
    well-known <code>./configure</code> script. As we may be doing
    cross-compilation, <code>target</code>, <code>host</code> and
    <code>build</code> arguments are given. The prefix is also set to
    <code>/usr</code>, not because the software will be installed in
    <code>/usr</code> on your host system, but in the target
    filesystem. Finally it creates a <code>.configured</code> file to
    mark the software as configured. </p>

    <p>Lines <a href="#line33">33-34</a> defines a target and a rule that 
    compiles the software. This target will create the binary file in the
    compilation directory, and depends on the software being already
    configured (hence the reference to the <code>.configured</code>
    file). It basically runs <code>make</code> inside the source
    directory. </p>

    <p>Lines <a href="#line36">36-38</a> defines a target and associated rules 
    that install the software inside the target filesystem. It depends on the
    binary file in the source directory, to make sure the software has
    been compiled. It uses the <code>install</code> target of the
    software <code>Makefile</code> by passing a <code>prefix</code>
    argument, so that the <code>Makefile</code> doesn't try to install
    the software inside host <code>/usr</code> but inside target
    <code>/usr</code>. After the installation, the
    <code>/usr/man</code> directory inside the target filesystem is
    removed to save space. </p>

    <p>Line <a href="#line40">40</a> defines the main target of the software, 
    the one that will be eventually be used by the top level
    <code>Makefile</code> to download, compile, and then install
    this package. This target should first of all depends on all
    needed dependecies of the software (in our example,
    <i>uclibc</i> and <i>ncurses</i>), and also depend on the
    final binary. This last dependency will call all previous
    dependencies in the correct order. </p>

    <p>Line <a href="#line42">42</a> defines a simple target that only 
    downloads the code source. This is not used during normal operation of 
    Buildroot, but is needed if you intend to download all required sources at 
    once for later offline build. Note that if you add a new package providing
    a <code>foo-source</code> target is <i>mandatory</i> to support
    users that wish to do offline-builds. Furthermore it eases checking
    if all package-sources are downloadable. </p>

    <p>Lines <a href="#line44">44-46</a> define a simple target to clean the 
    software build by calling the <i>Makefiles</i> with the appropriate option.
    The <code>-clean</code> target should run <code>make clean</code>
    on $(BUILD_DIR)/package-version and MUST uninstall all files of the
    package from $(STAGING_DIR) and from $(TARGET_DIR). </p>

    <p>Lines <a href="#line48">48-49</a> define a simple target to completely 
    remove the directory in which the software was uncompressed, configured and
    compiled. The <code>-dirclean</code> target MUST completely rm $(BUILD_DIR)/
    package-version. </p>

    <p>Lines <a href="#line51">51-58</a> adds the target <code>foo</code> to 
    the list of targets to be compiled by Buildroot by first checking if
    the configuration option for this package has been enabled
    using the configuration tool, and if so then &quot;subscribes&quot;
    this package to be compiled by adding it to the TARGETS
    global variable.  The name added to the TARGETS global
    variable is the name of this package's target, as defined on
    line <a href="#line40">40</a>, which is used by Buildroot to download, 
    compile, and then install this package. </p>


    <h3>Conclusion</h3>

    <p>As you can see, adding a software to buildroot is simply a
    matter of writing a <i>Makefile</i> using an already existing
    example and to modify it according to the compilation process of
    the software. </p>

    <p>If you package software that might be useful for other persons,
    don't forget to send a patch to Buildroot developers !</p>

     <h2><a name="links" id="links"></a>Resources</h2>

    <p>To learn more about Buildroot you can visit these
    websites:</p>

    <ul>
      <li><a href="http://www.uclibc.org/">http://www.uclibc.org/</a></li>
      <li><a href="http://www.busybox.net/">http://www.busybox.net/</a></li>
    </ul>

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